Linear induction electric motor

ABSTRACT

A linear electric induction motor has at least one stator or primary winding having a transverse winding axis and a predetermined pole pitch and a cooperating rotor or secondary member having a cross-section which is unsymmetrical about the transverse axis of the stator. The rotor or secondary member is provided with a pluraliry of apertures in the form of slots aligned in the direction of traction of the rotor, so as to obviate expulsive forces arising on account of asymmetry of rotor cross-section and adversely influencing the rotor member thereby causing undesirable friction and loss of power. The length of each of the slots is advantageously made longer than the winding pole pitch and the interspace between the slots is expediently made less than the stator pole pitch.

F'IP8502 United States Patent Izhelya et al.

[54] LINEAR INDUCTION ELECTRIC MOTOR [76] Inventors: Georgy IgnatievichIzhelya, Bulvar Lesi Ukrainki 24; Alexandr Grigorievich Shapovalenko,Ulitsa Zatonskogo 15/14; Vasily Ivanovich Shevchenko, Ulitsa Vernadskogo75; Vladimir Sergeevich Popkov, Ulitsa Dorogozhitskaya 21, all of Kiev,USSR.

[22 Filed: Feb. 16, 1972 [21] App]. No.: 226,922

[52] US. Cl. 310/13 [51] Int. Cl. H02k 41/02 [58] Field of Search 310/1214;

[56] References Cited UNITED STATES PATENTS 3,648,084 3/1972 Laithwaiteet a1..... 310/13 3,610,972 10/1971 Pelenc 310/13 2,731,212 1/1956 Baker310/12 UX Laithwaite 310/13 Ward et al 310/12 UX [57] ABSTRACT A linearelectric induction motor has at least one stator or primary windinghaving a transverse winding axis and a predetermined pole pitch and acooperating rotor or secondary member having a cross-section which isunsymmetrical about the transverse axis of the stator. The rotor orsecondary member is provided with a pluraliiy of apertures in the formof slots aligned in the direction of traction of the rotor, so as toobviate expulsive forces arising on account of asymmetry of rotorcross-section and adversely influencing the rotor member thereby causingundesirable friction and loss of power. The length of each of the slotsis advantageously made longer than the winding pole pitch and theinterspace between the slots is expediently made less than the statorpole pitch.

5 Claims, 2 Drawing Figures LINEAR INDUCTION ELECTRIC MOTOR BACKGROUNDOF THE INVENTION 1. Field of the Invention The present invention relatesto linear induction electric motors used for direct conversion ofelectric energy into mechanical energy of progressive translatory motionof the operating member in a machine or a mechanism.

2. Description of Prior Art Known in the art is a linear induction motorcomprising an elongated stator or primary inductor winding and a rotoror secondary member mounted asymmetrically with respect to a transverseaxis of the stator said rotor being provided with slots that are made inits surface to reduce the expulsive forces appearing due to theasymmetrical position of the rotor.

When a rotor with a continuous and uniform cross section along the wholeof its height (said height being measured perpendicular to the directionof traction) is arranged asymmetrically with respect to the stator, thecurrent flowing along the rotor is distributed nonuniformly. As isknown, this non-uniform current distribution produces expulsive forcesacting perpendicular to the tractive force. These forces aresufficiently strong; frequently they increase friction and causeaccelerated wear-out of the associated moving parts.

To reduce the above forces that tend to expulse the rotor, the latter issometimes arranged symmetrically with respect to the stator transverseaxis. In most cases this, however, leads to the weakening of parts thatbrace the stator mechanically and to excessive consumption of thenon-ferrous metal used to manufacture the rotor.

SUMMARY OF THE INVENTION The object of the present invention is toobviate the above disadvantages.

A specific object of the invention is to provide a linear inductionelectric motor of sufficient mechanical robustness and rigidity in whichthe above mentioned forces expulsing the rotor in a directionperpendicular to the action of the tractive force will be almost totallyeliminated.

This object is achieved in a linear induction electric motor in which,according to the invention, the slots in the rotor are arranged alongits length and the expul sive forces therefore are greatly reduced.

To eliminate the expulsive forces more effectively, it is advisable thatthe length of the slots running along the rotor should be increased, andthe interspace between the slots should be less than the pole pitch ofthe stator.

In order to prevent nonuniformity of rotor current distribution, it isdesirable to have the length of a slot substantially equal to andexceeding that of the pole pitch. Also, in order to limit the nonuniformcurrent distribution, it is expedient to limit the interspace betweenslots to less than the pole pitch of the winding.

The present invention can find applications in devices and mechanismswhere transverse forces produced by linear induction electric motors areundesirable since they can, for instance, result in undesirableresisting forces caused by friction. An example of such an applicationwould be a towing carriage ofa stand for ship model hydrodynamic tests.The linear motor in this case is mounted on top the carriage (it can notbe attached to the carriage from below since it is impossible to placethe rotor below the carriage where it would hamper the towing of themodel).

BRIEF DESCRIPTION OF THE DRAWING The invention will be better understoodfrom a more detailed description of the linear induction electric motorof the present invention with reference to the accompanying drawings inwhich:

FIG. Ipresents a side view of a linear induction electric motor, and

FIG. 2 is a front view of a linear induction electric motor.

DESCRIPTION OF PREFERRED EMBODIMENT As is shown in FIGS. 1 and 2, thelinear induction electric motor of the invention comprises an elongatedstator including two sections respectively having windings l and 2 and amoving member 3 corresponding to the rotor and placed between them.

The upper and the lower parts of the cross-section of rotor 3 areasymmetric with respect to the plane of symmetry of the stator. Thestator sections 1 and 2 are joined together with the aid of holders 4.They can alternatively be fixed on a suitable mount. To eliminate forcesthat tend to expulse the rotor 3 out of the interstator gap in adirection normal to the direction of traction the rotor 3 is providedwith longitudinal slots 5 and the length of each slot should be eitherequal to, or greater than, the pole pitch 1- of the stator (the width ofthe slots 5 produces no effect on the reduction of the expulsiveforces), while the interspace between the said slots is expediently lessthan the pole pitch 1 of the stator.

An alternating current flowing through the windings of the statorsections 1 and 2 produces a travelling magnetic field which spatiallytravels along the lengths stators l and 2 and along the length of therotor 3. The travelling magnetic field induces an electro-motive forcein the rotor 3 and creates electric currents which close within the polepitch 1 Since the length of the longitudinal slots 5 in the rotor 3 inaccordance with the invention are either equal to or greater than thepole pitch 7, these currents can not in fact get to the non-operatingsection of the rotor 3 beyond the slots 5. The magnetic field of therotor 3, therefore, becomes symmetrical with respect to the magneticfield of the stators 1 and 2. Hence, no resultant expulsive force isproduced since the distribution of longitudinal currents flowing throughrotor areas on both sides of the symmetry axis of the stator sections isidentical.

The arrangement of slots in the rotor described above will be just aseffective in eliminating the rotor expulsive forces in case when thelinear electric motor has only one stator section instead of two asillustrated in the exemplary embodiment.

What is claimed is:

1. A linear induction electric motor comprising: a primary windingconstituting the stator, said primary winding having at least onewinding section and a transverse axis and a predetermined pole pitch, asecondary member constituting a rotor and having a cross sectionasymmetrical with respect to said transverse axis of said at least onewinding section, said rotor being provided with a plurality of alignedslots formed along a length thereof, thereby reducing the forces thatexpulse said winding section.

4. A linear induction electric motor as claimed in claim 1, whichincludes two winding sections constituting the primary winding anddisposed one on either side of the rotor.

5. A linear induction electric motor as claimed in claim 4, furtherincluding means for holding and secur ing said two winding sections.

1. A linear induction electric motor comprising: a primary windingconstituting the stator, said primary winding having at least onewinding section and a transverse axis and a predetermined pole pitch, asecondary member constituting a rotor and having a cross sectionasymmetrical with respect to said transverse axis of said at least onewinding section, said rotor being provided with a plurality of alignedslots formed along a length thereof, thereby reducing the forces thatexpulse said rotor in a direction normal to the action of the tractiveforce on the rotor.
 2. A linear induction electric motor as of claim 1,in which the length of said longitudinal slots in the rotor exceeds thatof the pole pitch of the stator winding section, while the interspacebetween said slots is less than said pole pitch.
 3. A linear inductionelectric motor as claimed in claim 1, in which said slots are providedasymmetrically with respect to said transverse axis of said at least onewinding section.
 4. A linear induction electric motor as claimed inclaim 1, which includes two winding sections constituting the primarywinding and disposed one on either side of the rotor.
 5. A linearinduction electric motor as claimed in claim 4, further including meansfor holding and securing said two winding sections.